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A novel processing technology for the fabrication of particle reinforced metal matrix composites, powder thixoforming (PTF), was proposed and 6061 Al-based composites reinforced with 10% volume fractions of SiC particles (SiCp) were fabricated. The effects of processing parameters, such as reheating time, mould temperature and reheating temperature, on its microstructure and mechanical properties were investigated. The results indicated that all the three processing parameters exerted a significant influence on the microstructure and mechanical properties. The behavior of SiCp changes with the processing parameters. The best comprehensive mechanical properties with an ultimate tensile strength (UTS) of 228 MPa, elongation of 5.3% and a Vickers hardness of 66.4 HV are obtained when the composite is thixoforged under the reheating temperature of 660 0C for 90 min and the mould temperature of 250 0C.

Powder thixoforming (PTF) was a promising processing technology that can be used to fabricate high strength particle reinforced aluminum matrix composites, and a pioneer 6061 matrix alloy was fabricated utilizing PTF to investigate its solution treatment behaviors. A comparison study with traditional permanent mold cast (PMC) 6061 alloy disclosed that PTF alloy showed significantly reduced pore amount with only 0.16% (3.50% for PMC alloy). During solution treatment, PTF alloy displayed a much quicker solutionization progress than PMC alloy because of coarse eutectic phases and primary dendrites in latter alloy, its peak values of 14.5%, 241 MPa and 195 MPa in elongation, ultimate tensile strength and yield strength were achieved at 560ºC, an enhancement of 81.3%, 33.9% and 97.0%, respectively, compared with as-fabricated alloy. The dissolution of eutectic phases plays a dominative role in the growth of the primary α phases and secondarily primary α phases within 535ºC. However, the coarsening after 535ºC is subject to a mixture model involving atom diffusion along grain boundaries and through the crystal lattice. The superior tensile strengths of PTF alloy than PMC alloy resulted from decreased grain size, enhanced solid solution strengthening, reduced porosities and decreased harmful effect of insoluble phases in PTF alloy.

In this work, a novel processing method called powder thixoforming was proposed to prepare composites reinforced with 50 vol % of SiC particles (SiCp) that were used for electronic packaging in order to investigate the effects of remelting duration on its microstructure and properties. Optical Microscope (OM), Scanning Electron Microscope (SEM), X-ray Diffraction (XRD) and Transmission Electron Microscope (TEM) methods were applied for the material characterization and the corresponding physical and mechanical properties were examined in detail. The obtained results indicate that the remelting duration exerted a large effect on the microstructure as well as the SiCp/Al interfacial reaction. The density and hardness of the composite continuously increased with increasing remelting duration. The thermal conductivity (TC) and bending strength (BS) first increased during the initial 90 min and then decreased. The remelting duration exerted a limited influence on the coefficient of thermal expansion (CTE). The optimal TC, BS, and hardness of these composites were up to 135.79 W/(m·K), 348.53 MPa, and 105.23 HV, respectively, and the CTE was less than 6.5 ppm/K after the composites were remelted at 600 °C for 90 min. The properties of the composites could thus be controlled to conform to the application requirements for electronic packaging materials.

In this work, a novel processing method called powder thixoforming was proposed to prepare composites reinforced with 50 vol % of SiC particles (SiCp) that were used for electronic packaging in order to investigate the effects of remelting duration on its microstructure and properties. Optical Microscope (OM), Scanning Electron Microscope (SEM), X-ray Diffraction (XRD) and Transmission Electron Microscope (TEM) methods were applied for the material characterization and the corresponding physical and mechanical properties were examined in detail. The obtained results indicate that the remelting duration exerted a large effect on the microstructure as well as the SiCp/Al interfacial reaction. The density and hardness of the composite continuously increased with increasing remelting duration. The thermal conductivity (TC) and bending strength (BS) first increased during the initial 90 min and then decreased. The remelting duration exerted a limited influence on the coefficient of thermal expansion (CTE). The optimal TC, BS, and hardness of these composites were up to 135.79 W/(m·K), 348.53 MPa, and 105.23 HV, respectively, and the CTE was less than 6.5 ppm/K after the composites were remelted at 600 °C for 90 min. The properties of the composites could thus be controlled to conform to the application requirements for electronic packaging materials. [ABSTRACT FROM AUTHOR]

Microstructural and mechanical characterization of 10 vol% SiC particles (SiCp) reinforced 6061 Al-based composite fabricated by powder thixoforming (PTF) was investigated in comparison with the PTF and permanent mold cast (PMC) 6061 monolithic alloys. The results reveal that the microstructure of the PMC alloy consists of coarse and equiaxed α dendrites and interdendritic net-like eutectic phases. However, the microstructure of the PTF composite, similar to that of the PTF alloy, consists of near-spheroidal primary particles and intergranular secondarily solidified structures except SiCp, which are distributed in the secondarily solidified structures. The eutectics amount in the PTF materials is distinctly lower than that in the PMC alloy, and the microstructures of the former materials are quite compact while that of the latter alloy is porous. Therefore, the PTF alloy shows better tensile properties than the PMC alloy. Owing to the existence of the SiC reinforcing particles, the PTF composite attains an ultimate tensile strength and yield strength of 230 MPa and 128 MPa, representing an enhancement of 27.8% and 29.3% than those (180 MPa and 99 MPa) of the PTF alloy. A modified model based on three strengthening mechanisms was proposed to calculate the yield strength of the PTF composite. The obtained theoretical results were quite consistent with the experimental data. [ABSTRACT FROM AUTHOR]